Base for adjustable chairs

ABSTRACT

A compact base for vertically adjustable dental chairs. A linkage mechanism in the base is power operated, the motor unit and associated parts being disposed between the side members of the linkage mechanism and being substantially enclosed by such mechanism and other members of the base when the chair is in its lowered position. A one-way drive mechanism is provided, the chair traveling downwardly only under the influence of gravity when the motor is reversed. Increased safety upon lowering of the chair is thereby achieved because if the chair encounters an obstruction while moving downwardly, the applied forces will be limited to the gravity load. Such a construction also yields improved access for maintenance and assembly of the base.

United States Patent O sen [451 Oct. 17, 1972 1 BASE FOR ADJUSTABLECHAIRS 3,596,982 8/1971 Grams... ..297/330 IllVCIltOl'I Robert A. Olsen, Palatine, [731 Assign: A Hsl mll supply Corpm- 865,260 4/1961 Great Britain ..85/32 R Evanston 1,808,520 6/1970 Germany ..248/421 [22] Filed: Feb. 16, 1971 Primary Examiner-Marion Parsons, Jr. PP ,384 Att0rneyDaws0n, Tilton, Fallon & Lungmus 52 us. (:1. ..248/421, 74/89.15, 297/330 [57] ABSTRACT [51] Int. Cl..., ..A47c 1/04 A compact base for vertically adjustable dental chairs. [58] Field of Search ..248/421, 422, 404, 405, 406, A linkage mechanism in the base is power operated, 248/396; 74/8915; 297/330; 49/26, 28 the motor unit and associated parts being disposed between the side members of the linkage mechanism [56] References Cited and being substantially enclosed by such mechanism and other members of the base when the chair is in its UNITED STATES PATENTS lowered position. A one-way drive mechanism is pro- 521,256 6/1894 Browne ..248/421 Y g the if F Q dhwnwardly 2,337,902 12/1943 Lakin ..74/89.l5 Y e 3;? a l Y 'i'f g" 2,504,408 4/1950 Griffin ..,...74/89.l5 8a e Y e c ere Y achleved because if the cha1r encounters an obstruc- 2,614,672 10/1952 Launder ....49/26 2 685 812 8/1954 D ff 85/61 t1on while moving downwardly, the applied forces will 2929438 3/1960 31 5 "ga be limited to the gravity load. Such a construction also r r n 1 3,479,086 11/1969 Sheridan ..297/330 ggg access mamtenance and assemb y 3,505,888 4/1970 Denkowski ..74/89.l5 3,554,045 l/ 1971 Littmann ..49/28 16 Claims, 8 Drawing Figures l ll a i L 18 A r I (I I7 [A fl\ -4o 25 1 4o-- 27 29 1 23 O I 1 230 l (I) f I 26 28 1 1 (P (I) i 24 "20 i 21 /Hl v 1 I: I: l

u I. 3O 22 3| PATENTEU 17 3 6 98 .673

' sum 1 0r 3 INVENTORI ROBERT A. OLSEN ATT'YS PATENTEDIICT 1 7 I912 INVENTOR: ROBERT A. OLSEN BASE FOR ADJUSTABLE CHAIRS BACKGROUND Since modern dental techniques include operations that may be performed by a dentist while in a seated position as well as in the older and still common standing position, modern dental chairs, if they are to meet the needs and preferences of all dentists, must be capable of a substantial range of vertical movement. Furthermore, such movement should be achieved by an elevating mechanism of a self-contained base unit, in contrast to a unit which extends partially beneath a floor surface. Such a base must be compact, presenting no obstruction for a dentist operating in either a seated or standing position, and should be relatively simple, trouble-free and safe in structure and operation.

In general, prior efforts to achieve these objectives have been only partly successful. Thus, dental chair bases have been developed with folding linkage mechanisms which approach the goals of vertical adjustability and compactness. Such linkage-type bases are also self-contained, requiring no special sub-floor components. However, for all of their advantages, such units may in some instances be dangerous in use and, in general, such units are difficult and expensive to service and repair.

SUMMARY A main object of the present invention is to provide a dental chair base which has all of the main advantages of prior constructions without the aforementioned defects and disadvantages of such constructions. Specifically, it is an object to provide a compact base which is capable of shifting a chair over a wide range of vertical positions. Despite the compactness of the base, access to the power unit and power transfer components within such base, as well as to other major parts, may be easily and quickly achieved for purposes of inspection, service, and repair; Unlike other chairs which have positive power drive in both upward and downward directions, the present chair has a power unit which provides a positive or direct drive only in an upward direction. Descent of the chair is under the influence of gravity and, therefore, should the chair engage an obstruction as it is being lowered, damage or injury would be limited to that which might be caused by the gravity load.

These objectives are achieved by providing a base having a folding linkage mechanism, the mechanism consisting essentially of two substantially identical, vertical series of links extending between the seat-engaging member of the base and its floor-engaging member. The two series of links are positioned laterally apart to define a space therebetween, such space being at least partially occupied by the motor unit and by the power transfer means which transmits driving force from the motor to the linkage mechanism. The power transfer mechanism includes a screw shaft driven by the motor and means for preventing rotation of that shaft in response to downward or collapsing forces exerted upon the linkage mechanism. An important aspect of the invention lies in the fact that the power transfer mechanism also includes means which permits the linkage mechanism to be expanded manually when the motor is inoperative, or to be maintained in an ex- LII panded condition, as by some obstruction, when the motor is operated to lower the chair.

Other objects and advantages will appear from the specification and drawings.

DRAWINGS FIG. 1 is a perspective view of a dental chair equipped with a base construction of the present invention;

FIG. 2 is a sectional side view of the base taken along line 2-2 of FIG. 1, the expandable covering of the base being illustrated only in phantom to reveal the linkage mechanism in expanded condition;

FIG. 3 is a sectional side view similar to FIG. 2 but showing the linkage mechanism in a collapsed condition;

FIG. 4 is a top plan view of the base taken along line 4-4 of FIG. 3;

FIG. 5 is a perspective view of the base, the chair portion and the outer covering of the base being removed for clarity of illustration;

FIG. 6 is an enlarged side elevational view of the motor and power transfer mechanism;

FIG. 7 is a fragmentary horizontal sectional view taken along line 7-7 of FIG. 6;

FIG. 8 is a still further enlarged fragmentary vertical sectional view of the motor and power transfer mechanism illustrating the one-way clutch mechanism therefor.

DETAILED DESCRIPTION Referring first to FIG. 1, the numeral 10 generally designates an adjustable chair of the type commonly used for dental examination and treatment, the chair having a seat section 11 and a back rest section 12. A leg rest 13 is joined to the seat section and a head rest 14 is provided as an extension of the back rest. Arm rests 15 are mounted upon the back rest. The chair assembly includes a base 16 which is adapted to rest upon a floor surface and which is adjustable for the purpose of varying the elevation of the chair.

The base includes an upper seat-supporting member 17 which, as illustrated most clearly in FIG. 2, is connected by bolts 18 and brackets 19 to the seat section 11 of the chair. The base also includes a lower frame assembly consisting of frame members 20, base plate 21 and platform 22, the lower frame assembly being intended to rest or be mounted directly upon a floor surface. A linkage mechanism 23 is interposed between the lower frame assembly and the upper seat-supporting frame assembly for raising and lowering the chair as the linkage mechanism is extended and contracted.

The linkage mechanism consists essentially of two substantially identical sets or series 23a and 23b of links, the sets being positioned laterally apart to define a space therebetween in which motor unit 24 and its associated components are disposed. In the illustration given, the two sets or series of links are identical. As shown in FIG. 2, series 23a is composed of pivotally connected link elements 25, 26, 27, and 28, the opposite series 231; being composed of like elements. The two series are joined for simultaneous and identical movement by shaft 29, connecting assembly 30, and the upper and lower frame members 17 and 20 previously described.

The linkage assembly is extended and contracted or, more accurately, is extended and permitted to contract, by reversible motor 24 and by means for transmitting power from motor shaft 31 to the linkage mechanism. Such power transfer means includes a threaded drive shaft 32 which extends in a generally horizontal direction in the space between the upstanding sets of links 23a and 23b. The screw shaft is received in a threaded member 33 which is part of connecting assembly 30 (FIGS. 7, 6, 4). Recirculating ball bearings 33a are disposed within the threaded bore of member 33 so that friction between the parts will be reduced sufficiently to cause screw shaft 32 to rotate when member 33 is urged axially with respect thereto.

It is believed apparent that some means must be provided for preventing rotation of screw shaft 32 when member 33 is urged to the left as viewed in FIG. 6; otherwise the linkage mechanism 23 would close under the weight of the chair (and of its occupant) into the condition illustrated in FIG. 3. In the embodiment illustrated, the locking means for preventing such rotation of the shaft comprises the gear reduction assembly 34. The gear reduction assembly, which may take the form of a worm gear arrangement, is well known in the art and need not be described in detail herein. While other means for operatively interconnecting shafts 31 and 32, and for preventing rotation of shaft 31 in response to rotational forces imposed on shaft 32 might be used, a gear reduction assembly is particularly advantageous because it also achieves the objectives of reducing speed and increasing torque. I

Since the gear reduction assembly prevents the rotation of motor shaft 31 by rotational force applied to shaft 32, a one-way clutch mechanism 35 is interposed between shaft 32 and the gear reduction assembly 34 so that free rotation of shaft 32 will result when, forexample, seat 11 is manually raised to expand the linkage mechanism and to urge threaded member 33 to the right as viewed in FIG. 6. Any suitable one-way clutch mechanism may be provided, such mechanisms being entirely conventional and well known in the art. FIG. 8 illustrates one such mechanism in which a plurality of roller bearings 36 are interposed between an inner bearing race 37 operatively connected to the output shaft 38 of the gear reduction assembly and an outer race 39 operatively connected to screw shaft 32. As is well known, the surface of race 37 has undulations which permit rollers 36 to roll freely, without rotation of the race, when screw shaft 32 is rotated in one direction, but which wedge the roller bearings 36 between race 37 and race 39, to lock screw shaft 32 and output shaft 38 against independent rotation, when force is applied to rotate shaft 32 in the opposite direction.

The one-way clutch mechanism, combined with the ball-screw drive 32-34, not only permits the seat section of the chair to be raised manually, thereby expanding the linkage mechanism, but also performs an important safety function when the chair is to be lowered in normal operation. As previously indicated, such lowering is achieved simply by reversing motor 24 to rotate shafts 31 and 38 so that shaft 32 will in turn rotate and the chair will descend under the influence of gravity. It is to be emphasized that during such reverse rotation of motor 24 there is no direct drive of screw shaft 32; in-

stead, the screw shaft is caused to rotate by the gravity load imposed on the connecting assembly 30, the speed of rotation of the screw shaft being limited or braked by the speed of the power-driven motor shaft 31 and output shaft 38. Thus, should the descending chair encounter an obstacle which imposes a resistance greater than the weight of the chair and its occupant, if any, downward movement of the chair will cease even though motor 24 continues to operate. I

The fact that the chair is positively driven in only one direction, its upward direction, is also of considerable importance when adjustment, servicing, replacement, and repair of the motor 24 and of the components of the power train (ball-screw shaft assembly 32-33, oneway clutch 35, gear assembly 34) are required. With the linkage mechanism in the collapsed or contracted condition illustrated in FIGS. 3, 4 and 5, access to such elements would virtually be impossible, at least without unbolting and removing the seat of the chair from upper frame member 17. All of the components illustrated in FIG. 6 are disposed largely if not entirely in the space between the two sets of links 23a and 23b and, when the link assembly is collapsed, such components are confined by the two setsof contracted links, the lower frame 20 and its associatedparts, and the upper frame 17 and the seat connected thereto. However, when the linkage assembly is in the expanded condition illustrated in FIG. 2, such components are readily accessible for inspection, repair, or replacement (after raising or lowering the decorative and protective tubular sleeve 40 shown in phantom). Consequently, to gain access to such parts for servicing or repair when the chair is in a lowered position and motor 24 is inoperative, the seat or upper portion of the chair is simply raised manually to expand the link mechanism 23 and to expose the elementsof the power train.

While in the foregoing I have disclosed an embodiment of the invention in considerable detail for purposes of iliustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

I claim:

1. A compact base assembly for a vertically adjustable chair, comprising an upper frame member adapted to be connected to the underside of the seat portion of a chair, a lower frame member adapted to be supported upon a floor surface, an expandable and contractable linkage mechanism including two upstanding sets of links positioned laterally apart to define a space therebetween, each of said sets being operatively connected to both said upper and lower frame members for raising and lower said upper member as said linkage mechanism is expanded and contracted, a motor at least partially disposed in said space, and power transfer means operatively interconnecting said motor and said linkage mechanism for selectively expanding and contracting said mechanism as said motor is operated, said power transfer means including a oneway clutch capable of disengaging when an opposing upward force exceeding a predetermined magnitude is exerted upon said upper frame member, thereby permitting. manual expansion of said linkage mechanism when said motor is not operating and preventing contraction of said mechanism when said opposing force restrains downward movement of said upper frame member during operation of said motor.

2. The structure of claim 1 in which said power transfer means includes a screw shaft operatively connected to said motor for rotation thereby, and a movable member threaded upon said shaft and operatively connected to said linkage mechanism for expansion and contraction of said mechanism as said shaft is rotated in opposite directions.

3. The structure of claim 2 in which said movable member contains a plurality of ball bearings engaging the threads of said shaft for reducing friction to an extent wherein axial force upon said movable member tends to cause rotation of said screw shaft, said power transfer means also including a self-locking gear assembly and a one-way clutch interposed between said gear assembly and said screw shaft to permit independent rotation of said screw shaft in one direction relative to said gear assembly in response to the application of said upward opposing force upon said upper frame member.

4. The structure of claim 1 in which at least a substantial portion of said power transfer means is disposed within said space.

5. The structure of claim 4 in which said motor and said power transfer means are substantially confined by said linkage mechanism and said upper and lower frame members when said linkage mechanism is collapsed.

6. A base for a vertically adjustable chair, comprising an upper frame member, a lower frame assembly adapted to rest upon a floor surface, an expandable and contractable linkage mechanism including two substantially identical upstanding sets of links positioned laterally apart to define a space between said sets, each of said sets being operatively connected to both said upper and lower frame members for raising and lowering said upper member as said mechanism is expanded and contracted, a motor equipped with a gear reduction assembly having an output shaft, said gear reduction assembly being self-locking to prevent rotation of said output shaft when said motor is de-energized, a screw shaft and a movable member threadedly carried thereby, said movable member being adapted for rotating said screw shaft upon the application of axial force thereagainst and being operatively connected to said linkage mechanism for expanding and contracting the same when said screw shaft is rotated in opposite directions, and a one'way clutch interconnecting said screw shaft and said output shaft, said one-way clutch being engaged when force is exerted upon said upper frame member in the direction of gravitational force and automatically disengaging when a force of predetermined magnitude is exerted upon said upper frame member in opposition to gravitational force.

7. The structure of claim 6 in which said motor, screw shaft, movable member, and one-way clutch are disposed substantially entirely within said space.

8. The structure of claim 7 in which said motor, screw shaft, movable member, and one-way clutch are substantially enclosed by said linkage mechanism, said upper frame member, and said lower frame assembly, when said linkage mechanism is collapsed.

9. A vertically adjustable chair having a seat portion and a base disposed therebelow; said base comprising an upper frame member connected to the underside of said seat portion, a lower frame member adapted to be supported upon a floor surface, and an expandable and contractable linkage mechanism including two upstanding sets of links positioned laterally apart to define a space therebetween; each of said sets of links being operatively connected to both said upper and lower frame members for raising and lowering said seat portion as said linkage mechanism is expanded and contracted; a motor at least partially disposed in said spacebetween said sets of links; and power transfer means operatively interconnecting said motor and said linkage mechanism for selectively expanding and contracting said mechanism as said motor is operated; said power transfer means including a one-way clutch capable of disengaging when an opposing upward force exceeding a predetermined magnitude is exerted upon the seat portion of said chair, thereby permitting manual expansion of said linkage mechanism when said motor is not operating and preventing contraction of said mechanism when an opposing force restrains downward movement of said seat portion during operation of said motor.

10. The structure of claim 9 in which said power transfer means includes a screw shaft operatively'connected to said motor for rotation thereby, and a movable member threaded upon said shaft and operatively connected to said linkage mechanism for expansion and contraction of said mechanism as said shaft is rotated in opposite directions.

11. The structure of claim 10 in which said movable member includes a plurality of bearings engaging the threads of said shaft for reducing friction to an extent wherein axial force upon said movable member tends to rotate said screw shaft, said power transfer means also including a self-locking gear assembly and a oneway clutch interposed between said gear assembly and said screw shaft for permitting independent rotation of said screw shaft in one direction relative to said gear assembly in response to the application of said upward force upon said seat portion.

12. The structure of claim 9 in which at least a substantial portion of said power transfer means is disposed within said space.

13. The structure of claim 12 in which said motor and said power transfer means are substantially enclosed by said linkage mechanism and said upper and lower frame members when said linkage mechanism is collapsed. I

14. A vertical adjustable chair having a seat portion and a base; said base including an upper frame member secured to said seat portion, a lower frame assembly adapted to rest upon a floor surface, and an expandable and contractable linkage mechanism including two substantially identical upstanding sets of links positioned laterally apart to define a space between said sets; each of said sets being operatively connected to said upper frame member and said lower frame assembly for raising and lowering said seat portion as said mechanism is expanded and contracted; a motor equipped with a gear reduction assembly having an output shaft; said gear reduction assembly being selflocking to prevent rotation of said output shaft when is exerted upon said seat gravitational force.

15. The structure of claim 14 in which said motor, screw shaft, movable member, and one-way clutch are disposed substantially entirely within said space.

16. The structure of claim 14 in which said motor, screw shaft, movable member, and one-way clutch are substantially enclosed by said linkage mechanism, said upper frame member, and said lower frame assembly when said linkage mechanism is collapsed.

portion in opposition to 

1. A compact base assembly for a vertically adjustable chair, comprising an upper frame member adapted to be connected to the underside of the seat portion of a chair, a lower frame member adapted to be supported upon a floor surface, an expandable and contractable linkage mechanism including two upstanding sets of links positioned laterally apart to define a space therebetween, each of said sets being operatively connected to both said upper and lower frame members for raising and lower said upper member as said linkage mechanism is expanded and contracted, a motor at least partially disposed in said space, and power transfer means operatively interconnecting said motor and said linkage mechanism for selectively expanding and contracting said mechanism as said motor is operated, said power transfer means including a one-way clutch capable of disengaging when an opposing upward force exceeding a predetermined magnitude is exerted upon said upper frame member, thereby permitting manual expansion of said linkage mechanism when said motor is not operating and preventing contraction of said mechanism when said opposing force restrains downward movement of said upper frame member during operation of said motor.
 2. The structure of claim 1 in which said power transfer means includes a screw shaft operatively connected to said motor for rotation thereby, and a movable member threaded upon said shaft and operatively connected to said linkage mechanism for expansion and contraction of said mechanism as said shaft is rotated in opposite directions.
 3. The structure of claim 2 in which said movable member contains a plurality of ball bearings engaging the threads of said shaft for reducing friction to an extent wherein axial force upon said movable member tends to cause rotation of said screw shaft, said power transfer means also including a self-locking gear assembly and a one-way clutch interposed between said gear assembly and said screw shaft to permit independent rotation of said screw shaft in one direction relative to said gear assembly in response to the application of said upward opposing force upon said upper frame member.
 4. The structure of claim 1 in which at least a substantial portion of said power transfer means is disposed within said space.
 5. The structure of claim 4 in which said motor and said power transfer means are substantially confined by said linkage mechanism and said upper and lower frame members when said linkage mechanism is collapsed.
 6. A base for a vertically adjustable chair, comprising an upper frame member, A lower frame assembly adapted to rest upon a floor surface, an expandable and contractable linkage mechanism including two substantially identical upstanding sets of links positioned laterally apart to define a space between said sets, each of said sets being operatively connected to both said upper and lower frame members for raising and lowering said upper member as said mechanism is expanded and contracted, a motor equipped with a gear reduction assembly having an output shaft, said gear reduction assembly being self-locking to prevent rotation of said output shaft when said motor is de-energized, a screw shaft and a movable member threadedly carried thereby, said movable member being adapted for rotating said screw shaft upon the application of axial force thereagainst and being operatively connected to said linkage mechanism for expanding and contracting the same when said screw shaft is rotated in opposite directions, and a one-way clutch interconnecting said screw shaft and said output shaft, said one-way clutch being engaged when force is exerted upon said upper frame member in the direction of gravitational force and automatically disengaging when a force of predetermined magnitude is exerted upon said upper frame member in opposition to gravitational force.
 7. The structure of claim 6 in which said motor, screw shaft, movable member, and one-way clutch are disposed substantially entirely within said space.
 8. The structure of claim 7 in which said motor, screw shaft, movable member, and one-way clutch are substantially enclosed by said linkage mechanism, said upper frame member, and said lower frame assembly, when said linkage mechanism is collapsed.
 9. A vertically adjustable chair having a seat portion and a base disposed therebelow; said base comprising an upper frame member connected to the underside of said seat portion, a lower frame member adapted to be supported upon a floor surface, and an expandable and contractable linkage mechanism including two upstanding sets of links positioned laterally apart to define a space therebetween; each of said sets of links being operatively connected to both said upper and lower frame members for raising and lowering said seat portion as said linkage mechanism is expanded and contracted; a motor at least partially disposed in said space between said sets of links; and power transfer means operatively interconnecting said motor and said linkage mechanism for selectively expanding and contracting said mechanism as said motor is operated; said power transfer means including a one-way clutch capable of disengaging when an opposing upward force exceeding a predetermined magnitude is exerted upon the seat portion of said chair, thereby permitting manual expansion of said linkage mechanism when said motor is not operating and preventing contraction of said mechanism when an opposing force restrains downward movement of said seat portion during operation of said motor.
 10. The structure of claim 9 in which said power transfer means includes a screw shaft operatively connected to said motor for rotation thereby, and a movable member threaded upon said shaft and operatively connected to said linkage mechanism for expansion and contraction of said mechanism as said shaft is rotated in opposite directions.
 11. The structure of claim 10 in which said movable member includes a plurality of bearings engaging the threads of said shaft for reducing friction to an extent wherein axial force upon said movable member tends to rotate said screw shaft, said power transfer means also including a self-locking gear assembly and a one-way clutch interposed between said gear assembly and said screw shaft for permitting independent rotation of said screw shaft in one direction relative to said gear assembly in response to the application of said upward force upon said seat portion.
 12. The structure of claim 9 in which at least a substantial portion of said power transfer means is disposed within said space.
 13. The structure of claim 12 in which said motor and said power transfer means are substantially enclosed by said linkage mechanism and said upper and lower frame members when said linkage mechanism is collapsed.
 14. A vertical adjustable chair having a seat portion and a base; said base including an upper frame member secured to said seat portion, a lower frame assembly adapted to rest upon a floor surface, and an expandable and contractable linkage mechanism including two substantially identical upstanding sets of links positioned laterally apart to define a space between said sets; each of said sets being operatively connected to said upper frame member and said lower frame assembly for raising and lowering said seat portion as said mechanism is expanded and contracted; a motor equipped with a gear reduction assembly having an output shaft; said gear reduction assembly being self-locking to prevent rotation of said output shaft when said motor is de-energized; a screw shaft and a movable member threadedly carried thereby; said movable member being adapted for rotating said screw shaft upon the application of axial force against said movable member and being operatively connected to said linkage mechanism for expanding and contracting the same when said screw shaft is rotated in opposite directions; and a one-way clutch interconnecting said screw shaft and said output shaft; said one-way clutch being engaged when force is exerted upon said seat portion in the direction of gravitational force and automatically disengaging when a force of predetermined magnitude is exerted upon said seat portion in opposition to gravitational force.
 15. The structure of claim 14 in which said motor, screw shaft, movable member, and one-way clutch are disposed substantially entirely within said space.
 16. The structure of claim 14 in which said motor, screw shaft, movable member, and one-way clutch are substantially enclosed by said linkage mechanism, said upper frame member, and said lower frame assembly when said linkage mechanism is collapsed. 